By June 11, 2021, the number of vaccinations in China had exceeded 860 million doses; Domestic enterprises have long launched various antibody testing products, including total antibody and neutralizing antibody testing. For the evaluation of vaccine effect, the best method is the detection of neutralizing antibody. However, so far, no study has defined the concentration of neutralizing antibody to protect the new crown, so the current detection is still based on qualitative detection, that is, to judge the presence or absence of antibody.

The World Health Organization (who) released the first generation international standard of new crown antibody (NIBSC Code: 20 / 136) through the collaborative calibration among international laboratories, and determined the international unit concentration of neutralizing antibody, which laid a foundation for subsequent quantitative research. In the next step, the effective protective concentration of new crown neutralizing antibody can be determined through research, For example, the critical value of hepatitis B virus surface antibody is 10miu / ml.

In addition to 20 / 136, who also launched two other new crown antibody related products, namely 20 / 268 and 20 / 130, namely international reference disk and quality control products for R & D.

Today, let's talk about the two basic concepts of how to use these products

1) The difference between new crown antibody detection and new crown antibody neutralizing antibody detection.

If there is no special description, the new crown antibody detects the total antibody, including antibodies of different subtypes such as IgG and IgM, and different antigen epitopes (antigens selected according to the product), while the neutralizing antibody is only a part of the total antibody. Neutralizing antibody is a kind of antibody that can bind to the virus and lose its infectivity stimulated by the outermost envelope or capsid antigen of the virus. The mechanism of neutralizing antibody generally includes changing the surface configuration of virus; Binding of virus epitopes related to adsorption prevents virus adsorption, so that the virus can not invade cells for proliferation; It forms immune complex with virus and is easy to be swallowed and cleared by macrophages; After the surface antigen of the enveloped virus binds to the neutralizing antibody, the complement is activated, which can lead to the dissolution of the virus. This is why neutralizing antibody detection is one of the important indicators in vaccine development and clinical evaluation.

2) Detection method of neutralizing antibody

The gold standard method of neutralizing antibody is neutralization test, that is, live virus or synthetic virus is used to react with the sample to detect the killing ability of neutralizing antibody to virus in the sample. This method is used in the clinical effect evaluation of vaccine published now. However, this method has high requirements for testing, and is not suitable for popularization and use in ordinary medical testing institutions.

Another kind of neutralizing antibody detection is to use the principle of immune reaction to detect the corresponding neutralizing antibody through specific antigen. Generally speaking, it is to "identify" the neutralizing antibody from the total antibody of the new crown. This method is suitable for the promotion and use of ordinary medical testing institutions, and the key lies in the selection of antigen.

Who's three products on new crown antibodies

1) Three different new crown antibody products of who are shown in Table 1

Table 1 who three different new crown antibody products

2) 20 / 136 and 20 / 268.

From July to October 2020, who collected the results of 125 methods from 44 laboratories in 15 countries for collaborative calibration; Because of the problem of sample entry permission, 3 Chinese mainland laboratories that had planned to participate in collaborative calibration failed to participate. China was only a laboratory in University of Hong Kong. The collaborative calibration of neutralizing antibody concentration summarizes the results of 27 neutralization test methods, of which 15 methods use natural viruses and the rest use synthetic viruses; The results of 98 methods were summarized, including 78 ELISA methods, 16 flow cytometry, 2 immunochromatography and 2 inhibition tests; The antigens were mainly RBD, S1, N and spike proteins. The detected subtypes were mainly total antibody or IgG, IgM (3 methods) and IgA (5 methods).

The collaborative calibration group set the neutralizing antibody concentration and binding antibody concentration of international standard 20 / 136 at 1000, and the units are IU / ml (international units) and Bau / ml (binding antibody units) respectively; It should be noted that although they are all 1000, the neutralizing antibody and binding antibody units are different, and the actual concentration is also different; The reactivity of binding antibodies against different antigen classes is also different, but they are all assigned 1000.

The four samples in the international reference disk 20 / 268 were assigned with a concentration unit of 20 / 136 of 1000 to determine the different antibody concentrations of each sample, including neutralizing antibody and IgG concentration for four different antigens (RBD, S1, N and spike) (IgA and IgM cannot be statistically analyzed due to too few data). The four samples covered different concentrations of high, medium and low.

For diagnostic reagent manufacturers, when developing quantitative products, they should first trace the quantity value of the products with 20 / 136, then evaluate the reagents with 20 / 268, and evaluate the accuracy of the products according to the corresponding concentration according to the type of antibody detected by the products. 20 / 130 can be used in the R & D process, but it can not be used to evaluate the quantitative accuracy.

reference:

1）Mattiuzzo et al. Establishment of the WHO International Standard and Reference Panel for anti-SARS-CoV-2 antibody. 2020, WHO Expert Committee on Biological Standardization. WHO/BS/2020.2403；

2） First WHO International Standard for anti-SARS-CoV-2 immunoglobulin (human) NIBSC code: 20/136 Instructions for use (Version 2.0, Dated 17/12/2020)；

3）First WHO International Reference Panel for anti-SARS-CoV-2 immunoglubulin NIBSC code: 20/268 Instructions for use (Version 3.0, Dated 17/12/2020)；

4）Research reagent for anti-SARS-CoV-2 Ab NIBSC code 20/130 (Version 2, Dated 17/01/2021)；

5) the center for examination and examination of New Coronavirus currently has several considerations on the neutralizing antibody detection reagent, 10/02/2021.